We will analyze the factors which can stimulate or inhibit the proliferation of vascular endothelial cells, as well as how these factors can be involved in the pathogenesis of vascular disease. In this respect, we will investigate the relationship between the morphological structure of the endothelium (highly contact-inhibited and flattened cell monolayer) and its role as a selective permeability barrier. We will focus on the mechanism of interaction of LDL and HDL with vascular endothelial cells, particularly their internalization and degradation. We will compare the endocytosis, which occurred in disrupted cell monolayer through the capping phenomenon to that which occurred in normal contact-inhibited vascular endothelial cell monolayer.